Respiratory syncytial virus (RSV) is a recurrent cause of severe respiratory tract infections in infants and very young children and causes annual epidemics during the winter months. RSV typically causes its primary infection at the point of entry: the ciliated epithelial cells that line the nasal cavity and airways (Black 2003, Respir. Care 48: 209-31; discussion 231-3). Primary infections are usually symptomatic with clinical signs ranging from mild upper respiratory tract illness to more severe lower respiratory tract infections (LRTIs), including bronchopneumonia and bronchiolitis (Aliyu, et al. 2010, Bayero Journal of Pure and Applied Sciences 3: 147-155), which occurs predominantly in infants.
The transmembrane glycoproteins F and G are the primary surface antigens of RSV. The attachment protein (G) mediates binding to cell receptors, while the F protein promotes fusion with cell membranes, allowing penetration into the host cell (Lopez et al. 1998, 72: 6922-8). Based on antigenic and genetic variability of the G protein, 2 serotypes of RSV have been identified (A and B), along with several subtypes.
In contrast to the G protein, the F protein is highly conserved between RSV serotypes A and B (89% amino acid identity), and is therefore considered the main target for development of viral entry inhibitors. Glycoprotein F also induces fusion of infected cells with adjacent uninfected cells. This hallmark feature results in the appearance of multinucleate cell formations (epithelial cell syncytia), which allow for cell-to-cell transmission of replicated viral ribonucleic acid (RNA), conferring additional protection against host immune responses (Black 2003).
RSV infection imposes a significant burden on health care infrastructure and there remains a high medical need for treatment options, especially since there is no vaccine available to prevent RSV infections.
The only drug product available in the market is a humanized monoclonal antibody (SYNAGIS® (palivizumab)) directed against the viral glycoprotein F which is used prophylactically in children that are at a very high risk of suffering a severe hRSV infection. The restricted use of SYNAGIS® is due, at least in part, to the high cost of this product. Since there are no adequate medications available for treatment of RSV infection, the standard of care for hospitalized infants is mostly supportive (e.g., fluid/feed supplementation, observation, and respiratory support as needed). There is clearly a need for improved and/or cheaper prophylactic and/or therapeutic agents for the prevention and/or treatment of infections by hRSV.
SEQ ID NOs: 65-85 of the present disclosure are immunoglobulin single variable domains directed against the fusion protein of the human respiratory syncytial virus. SEQ ID NOs: 65-85 consist of 3 anti-hRSV immunoglobulin single variable domains, recombinantly linked by a flexible linker.
SEQ ID NOs: 65-85 were extensively characterized in vitro and in vivo (see for example WO 2010/139808; the contents of which are incorporated by reference in their entirety). The anti-hRSV immunoglobulin single variable domains specifically and potently bind to the respiratory syncytial virus (RSV) F protein. In vitro micro-neutralization studies in HEp2 cells, suggested that these anti-hRSV immunoglobulin single variable domains inhibit an early event in the viral life cycle, preventing extracellular virus from infecting virus naïve cells. Efficacy of SEQ ID NOs: 65-85 was confirmed in RSV-infected cotton rats.
Since SEQ ID NOs: 65-85 are intended to neutralize and inhibit RSV, direct delivery and deposition in the respiratory tract through an aerosol device is considered the preferred and most suitable route of administration. Formulation of immunoglobulin single variable domains (including SEQ ID NOs: 65-85) as a nebulizer solution has been extensively described in WO 2011/098552.
The safety, tolerability and pharmacokinetic (PK) parameters of inhalation of SEQ ID NO: 71 have further been evaluated in three Phase I clinical studies in adult volunteers. These studies showed that inhalation and intravenous (i.v.) infusion of SEQ ID NO: 71 is generally well-tolerated. There is, however, no possibility for extrapolating efficacy from adults to children, or from older to younger children, as lower respiratory tract disease caused by RSV rarely occurs in these populations.